Toronto Blue Jays manager John Gibbons confirmed prior to Thursday's game that Marco Estrada has been pitching with a herniated disc in his back.
Gibbons said the problem is not new and has been known to the club for the entire season.
"Really, that's old news," Gibbons told reporters on Thursday. "He's had it since the beginning of spring training. My understanding is that anybody who has back problems, it's from a herniated disk on some level. It's what affects the nerve."
The diagnosis of the injury was first reported by MLB Network’s John Morosi earlier in the day.
Estrada’s back problems have persisted for months now. He was pulled from the All-Star Game in July and spent time on the disabled list.
"My worst nightmare came true, unfortunately," Estrada said after withdrawing from the mid-summer classic in San Diego. "In the long run, this is the right thing to do."
The rest was supposed to help, but Estrada (8-9, 3.78 ERA) has not been the same.
Since returning to the lineup on July 22, the 33-year-old is 3-6 and has thrown more than six innings in just two of 10 starts.
He has allowed 12 earned runs in his last 12 2/3 innings during a three game losing streak.
The Blue Jays have spiralled out of first in the AL East, falling behind both the Boston Red Sox and Baltimore Orioles with four wins in their last 12 games.